The use of whitening agents, either optical brighteners or blueing agents, in textile applications is well known in the prior art. As textile substrates age, their color tends to fade or yellow due to exposure to light, air, soil, and natural degradation of the fibers that comprise the substrates. Thus, the purpose of whitening agents is generally to visually brighten these textile substrates and counteract the fading and yellowing of the substrates. Typically, whitening agents may be found in laundry detergents, fabric softeners, or rinse aids and are therefore applied to textile substrates during the laundering process. However, it is important that whitening agents function to brighten treated textile substrates without causing undesirable staining.
Cellulosic substrates, in particular, tend to exhibit a yellow hue after exposure to light, air, and/or soiling. This yellowness is often difficult to reverse by normal laundering procedures. As a result, there exists a need for improved whitening agents which are capable of eliminating the yellowness exhibited by ageing textile substrates, and in particular cellulosic substrates. By utilizing such improved whitening agents, the life of the textile substrates, such as clothing articles, table linens, etc., may be extended.
The whitening agents of the present invention offer advantages over the prior art, including U.S. Pat. No. 4,137,243, U.S. Pat. No. 5,039,782 and US2005/0288206 as they take advantage of compounds having a hueing efficiency of at least 5 and a wash removal value in the range of from about 30% to about 95%. Such compounds can emit light with wavelengths in the range of blue, red, violet, purple, or combinations thereof upon exposure to ultraviolet light (or, they absorb light to produce the same shades) in order to neutralize the yellowness of cellulosic substrates. These compounds function ideally as whitening agents for cellulosic substrates and may be incorporated into laundry detergent formulations for use by consumers during the laundering process.
However, whilst the preferred whitening agents exhibit excellent whitening, they also make the composition, in which they are formulated, unappealingly dark. It is therefore an object of the present invention to provide a way to incorporate the high performing whitening agents in a liquid detergent product whilst circumventing this unappealing side effect.